3 ms·

thanks it’s good to know the fat can be opted out at compile time. I am very curious what a modern kernel contain that an old linux kernel did not that would ma

by skyde 6y ago

thanks it’s good to know the fat can be opted out at compile time. I am very curious what a modern kernel contain that an old linux kernel did not that would make it more than 30 times bigger

neurostimulant 6y ago
Raspberry pi kernel 4.14 on my pihole is around 4-5MB, linux 4.4 generic kernel in ubuntu 16.04 on one of my older box is around 6-7MB, and Linux 5.4 generic kernel on ubuntu 20.04 on my vps and desktop is around 12MB. Tuning down the size of the compiled linux kernel seem to be a sport of some sort, with many guides like this [0] available online. [0] https://elinux.org/Kernel_Size_Tuning_Guide https://elinux.org/Kernel_Size_Tuning_Guide
Teknoman117 6y ago
Three major areas - Device Drivers, Virtualization, and Network Filtering It's not so much fat as it is feature support and what's enabled by default. Most people want the "default" configuration to work out of the box on whatever computer they have. E.g. If you take a look at "x86_64_defconfig", nearly every Ethernet card that Linux supports is enabled. Odds are you only have one of those in your (desktop) system. However, unless you shopped around for specific NICs, odds are you don't own two systems that use the same ethernet driver. For those of us who want to only compile the support for exactly what we use, it is still possible to compile the kernel small enough to boot off of a 1.44 MiB floppy with a minimal initial ramdisk, assuming the system you want to use it on is old. Modern systems require so much more code to use the hardware in them, and as Linux has become the single most used operating system kernel on the planet, the amount of code for device drivers has grown astronomically. The kernel contains a minimal configuration called "tinyconfig" which turns off literally anything that be while retaining a functioning kernel. A tinyconfig kernel + TTY support compiles to about 500 KiB. Enabling all of the drivers to support hardware via the BIOS (AT style disk control, floppy, display out, etc.), and ELF support will yield a kernel of ~790 KiB, a little more than half of your 1.44 MiB floppy. Assuming you can fit useful userspace tools in the remaining space, you could still load from a floppy.
forty 6y ago
Drivers for all the hardware that was created in the meantime for example :)
- megous 6y ago
  That's usually compiled as modules.
jlgaddis 6y ago
> I am very curious what a modern kernel contain that an old linux kernel did not ... Um, perhaps support for all of the hardware, filesystems, network protocols, etc., that did not exist?
- Teknoman117 6y ago
  The only measure by which I believe it would be acceptable to judge Linux "fat" would be to compare the size of kernels generated using "tinyconfig". Basically, everything that can be disabled without rendering the kernel useless it turned off. You're only left with the core of the kernel. At this point in time, you get a kernel image that's like ~450 KiB. If you actually want to boot that on real hardware, you can enable the drivers that are stubs into the BIOS calls for classic devices (disks, serial ports, SVGA graphics, etc.) for another ~100 KiB. It's extremely limited though - no specific PCIe support, ACPI, networking, etc.

by skyde 6y ago

thanks it’s good to know the fat can be opted out at compile time. I am very curious what a modern kernel contain that an old linux kernel did not that would make it more than 30 times bigger

neurostimulant 6y ago

Raspberry pi kernel 4.14 on my pihole is around 4-5MB, linux 4.4 generic kernel in ubuntu 16.04 on one of my older box is around 6-7MB, and Linux 5.4 generic kernel on ubuntu 20.04 on my vps and desktop is around 12MB. Tuning down the size of the compiled linux kernel seem to be a sport of some sort, with many guides like this [0] available online. [0] https://elinux.org/Kernel_Size_Tuning_Guide https://elinux.org/Kernel_Size_Tuning_Guide

Teknoman117 6y ago

Three major areas - Device Drivers, Virtualization, and Network Filtering It's not so much fat as it is feature support and what's enabled by default. Most people want the "default" configuration to work out of the box on whatever computer they have. E.g. If you take a look at "x86_64_defconfig", nearly every Ethernet card that Linux supports is enabled. Odds are you only have one of those in your (desktop) system. However, unless you shopped around for specific NICs, odds are you don't own two systems that use the same ethernet driver. For those of us who want to only compile the support for exactly what we use, it is still possible to compile the kernel small enough to boot off of a 1.44 MiB floppy with a minimal initial ramdisk, assuming the system you want to use it on is old. Modern systems require so much more code to use the hardware in them, and as Linux has become the single most used operating system kernel on the planet, the amount of code for device drivers has grown astronomically. The kernel contains a minimal configuration called "tinyconfig" which turns off literally anything that be while retaining a functioning kernel. A tinyconfig kernel + TTY support compiles to about 500 KiB. Enabling all of the drivers to support hardware via the BIOS (AT style disk control, floppy, display out, etc.), and ELF support will yield a kernel of ~790 KiB, a little more than half of your 1.44 MiB floppy. Assuming you can fit useful userspace tools in the remaining space, you could still load from a floppy.

forty 6y ago

Drivers for all the hardware that was created in the meantime for example :)

megous 6y ago
That's usually compiled as modules.

jlgaddis 6y ago

> I am very curious what a modern kernel contain that an old linux kernel did not ... Um, perhaps support for all of the hardware, filesystems, network protocols, etc., that did not exist?

Teknoman117 6y ago
The only measure by which I believe it would be acceptable to judge Linux "fat" would be to compare the size of kernels generated using "tinyconfig". Basically, everything that can be disabled without rendering the kernel useless it turned off. You're only left with the core of the kernel. At this point in time, you get a kernel image that's like ~450 KiB. If you actually want to boot that on real hardware, you can enable the drivers that are stubs into the BIOS calls for classic devices (disks, serial ports, SVGA graphics, etc.) for another ~100 KiB. It's extremely limited though - no specific PCIe support, ACPI, networking, etc.